In FIG. 1 is shown a side view of a work implement in a heretofore known shovel-loader. In this figure, a lift arm d pivotably supported at a pivotal support section i of the lift arm on the side of a vehicle body a in an upwardly and downwardly rotatable manner, rotates upwards when a lift cylinder e extends, and a bucket c pivotably supported in a forwardly and backwardly tiltable manner at a bucket pivotable support section j at the tip end of the lift arm d, is tilted backwardly via a bellcrank f and a tilt rod h when a tilt cylinder is extended. Reference character b designates a tire. The state of the bucket shown at c in this figure is a state upon excavation of earth and sand, and a bucket bottom surface k is nearly parallel to a ground surface GL (horizontal). And, a vehible body connecting pivotable support section of the tilt cylinder g is designated by reference character l, a connecting pivotable support section on the side of the bellcrank f by character m, a connecting pivotable support section to the lift arm d of the bellcrank f by character n, a connecting pivotable support section between the bellcrank f and the tilt rod h by character p, a connecting pivotable support section between the tilt rod h and the bucket c by character g, a connecting pivotable support section on the side of the vehicle body of the lift cylinder e by character r, and a connecting pivotable support section on the side of the lift and d thereof by character s.
Thus, after excavation has been finished, a loading work starts, and when the lift cylinder e and the tilt cylinder g are extended in a desired manner, the bucket becomes the state shown at c.sub.1. If the centers of the above-described respective pivotable support sections when the bucket has moved from c to c.sub.1 are represented by movements of reference characters for simplicity of explanation, they are indicated by s.fwdarw.s.sub.1, j.fwdarw.j.sub.1, m.fwdarw.m.sub.1, n.fwdarw.n.sub.1, p.fwdarw.p.sub.1, q.fwdarw.q.sub.1 and k.fwdarw.k.sub.1.
Then, if the lift and d is further rotated upwards by operating the lift cylinder e and the bucket pivotable support section j is raised up to the highest position j.sub.2, the bucket comes to a position c.sub.2, and the respective pivotable support sections would come respectively to the positions designated by the same characters but having a suffix 2 (for instance, m.fwdarw.m.sub.2). Under this condition, if the tilt cylinder g is contracted in order to forwardly tilt the bucket, the respective pivotable support sections would come respectively to the positions designated by the same characters but having a suffix 3 (for instance, m.sub.2 .fwdarw.m.sub.3, but the positions of the sections n.sub.2, s.sub.2 and j.sub.2 would not change), and the bucket takes the state shown at c.sub.3.
This linkage mechanism in the prior art shown in FIG. 1 is a linkage generally called "Z-bar linkage", in which when the bucket takes the state shown at c in FIG. 1, if the tilt cylinder g is extended, the bucket bottom surface k would rotate in the direction shown by an arrow K, and at this time a hydraulic pressure in the bottom side pressure receiving chamber gb of the tilt cylinder g acts, and therefore, this linkage is that generally used in a loading vehicle which necessitates a large excavation force.
Though this linkage is designed so as to maintain a backwardly tilted state (designed for reducing tilt angle variations under a tilted state) so that loaded articles may not spill out even if the lift arm is rotated up and donw with the bucket held backwardly tilted (the state shown at c.sub.1 in FIG. 1) because it is mainly used for loading of earth and sand, it does not have a structure for eliminating tilt angle variations under a horizontal state of the bucket.
More particularly, one example of the operation when the bucket is held in parallel to the ground surface (held horizontal) as shown at c in FIG. 1 and the lift arm d is rotated upwards with the length of the tilt cylinder g at that time (the distance between l and m in that figure) maintained, is shown by a dash-line R in FIG. 4, in which at a certain instance at tilt angle .theta. with respect to the ground of the bucket bottom surface k changes by about 20.degree..
Consequently, in order to maintain a horizontal state of the bucket, upon rotating the lift arm the operation of extending and/or contracting the tilt cylinder is necessitated, and thus there was a disadvantage that the operation is troublesome and also a maneuverability was poor.